1. Field of the Invention
The present invention relates to a mobile station apparatus and base station apparatus using a CDMA (Code Division Multiple Access) system.
2. Description of the Related Art
In a CDMA (Code Division Multiple Access) based mobile communication system, in the case that a mobile station carries out handover to a mobile communication systems service using a different system (for example, FDMA system, TDMA system, etc.)(hereinafter simply referred to as a xe2x80x9cdifferent mobile communication systemxe2x80x9d) or handover to the same CDMA mobile communication system with a different carrier frequency, the mobile station needs to monitor information on the carrier of the handover destination before carrying out handover to carry it out smoothly.
FIG.1 is a schematic view of cells to explain the situation of the handover. Suppose there are 3 cells in this case. When mobile station 12 connected to base station 11 moves from cell 13 to cell 14 which is a cell of a different mobile communication system, the mobile station needs to receive a control channel signal transmitted by base station 15 of cell 14, the destination, and monitor the control channel of base station 15.
There are mainly two types of channels used in CDMA-based mobile communications, control channel and communication channel. A control channel signal is transmitted from a base station to all mobile stations in the same cell. A broadcast channel (BCCH) signal is mapped in the control channel signal, and the broadcast channel signal mainly contains synchronization-related information, downlink transmission power information and uplink interference power information, etc. A communication channel signal is transmitted/received between the base station and mobile station and the communication channel is a channel for communicating data comprising a message signal.
FIG. 2 is a schematic view showing frame structures of a communication channel signal and control channel signal that a conventional base station apparatus transmits. The communication channel signal is divided into frames of 10 msec, for example and these frames are further divided into 16 slots, for example. Such frame-structured communication channel signals are used for data communications. The broadcast channel signal is transmitted over one entire frame of the communication channel signal of 10 msec, for example.
Such a frame structure does not allow the mobile station to have a free time to monitor the carrier information of a different mobile communication system. Therefore, the conventional base station takes the following measure for a communication channel signal to be transmitted.
FIG. 3A, FIG. 3B and FIG. 3C are schematic views of frame structures of a transmission signal of a conventional base station apparatus. FIG. 3A shows a frame structure of a communication channel signal during a normal communication.
The frame structure during monitoring is explained using FIG. 3B and FIG. 3C. FIG. 3B shows a frame structure when transmitting data using the first half of one frame at a double transmission rate by adding one-frame information of the communication channel signal in the base station apparatus. FIG. 3C shows a frame structure when transmitting the added information in FIG. 3B using the front end and back end of the frame by dividing one frame into 4 parts in the base station apparatus.
In the case that the base station transmits the communication channel signal with such a frame structure to the mobile station, a blank time zone (hereinafter referred to as xe2x80x9cidle intervalxe2x80x9d) is produced in the frame as shown in the figure, and the mobile station on the receiving side has no data to be received in this idle interval. Therefore, the mobile station can use this idle interval in the communication channel to monitor a control channel of a different mobile communication system.
Therefore, the mobile station can establish synchronization at the time of handover based on the carrier information of a different mobile communication system at the handover destination received, making it possible to carry out smooth handover.
However, the conventional apparatus has problems as shown below: That is, the conventional base station transmits a frame-structured communication channel signal having an idle interval to the mobile station so as to provide the mobile station with an idle interval to receive the control channel signal at the handover destination. Therefore, the transmission signal from the base station has a blank time during which no data are sent, causing signal interruption on the radio communication line.
Furthermore, the conventional mobile station cannot perform correct reception or decoding unless it is notified beforehand of the timing with which added data with a high transmission rate are incoming, and it is necessary to assign new channel resources to transmit the timing-related information from the base station to mobile station. Therefore, In the case that there are not enough channel resources, it is difficult for the mobile station to receive the carrier information of the different mobile communication system.
It is an objective of the present invention to provide a mobile station apparatus and base station apparatus that form a blank time for the mobile station apparatus to receive a control channel signal of a different mobile communication system in a broadcast channel, causing no signal interruption of a radio communication line at the time of handover and without requiring assignment of further channel resources.
In order to achieve the objective above, the base station apparatus of the present invention compresses one-frame information of the broadcast channel signal to a block of xc2xd of one frame or less and repeatedly transmits this block during a one-frame time. On the other hand, the mobile station apparatus decodes these repeatedly transmitted blocks in block units or added block units and performs error detection and in the case that the error rate exceeds a threshold, it receives and adds up the next block. The mobile station apparatus repeats this operation until the error rate falls below the threshold. Furthermore, when the error rate falls below the threshold, the mobile station apparatus stops reception of broadcast channel signals and uses the rest of time until a one-frame time elapses to monitor a control channel of a different mobile communication system necessary for handover.